are hasty slings outlawed in the standing or something? I see no one using one
Slings are not allowed in Standing in NRA High Power nor CMP GSM Vintage Military Rifle Games.
They are also not allowed in NRA and ISU Small Bore.
In my 35 years of competition shooting I found that slings just get in the way in the standing position.
Use to be you had to have the sling in the parade position in off hand. Now they can be taken off the rifle.
Looking at the video you'll notice some had the slings attached and loose. That is something you need to watch. Its hard enough shooting offhand without the loose sling flowing in the breeze disturbing your rifle.
That was a good video of a GSM match. Most had some pretty solid postions. Notice the bolt gun shooters; you don't take the rifle out of your shoulder while working the bolt.
CMP sells shooting coats as well as mats. I use to use a heavy leather coat but pretty much went to a straigh cloth coat with the rubber on the shoulder and elbows. Same with a glove. If you get a glove get one with the rubber pads. They help keep your non shooting hand from sliding up and down on the stock.
The CMP has GSM Vintage Rifle clinics scattered across the country taught by CMP GSM Master Instructors. I higly recommend everyone attend one if interested in GSM Games or HP.